Gas turbine engines with can annular combustors require structures to conduct and direct the gasses from the combustors to the first row of turbine blades. These structures must orient the combustion gas flow streams to contact the turbine blades at an optimum angle for rotation of the blades. Conventional structures include transition ducts, stationary vanes, and seals. Each transition duct conducts gas from a combustor to the vanes which are immediately upstream of the blades. The vanes orient the gas flow circumferentially and direct it toward the blades.
This configuration reduces the amount of energy present in the gas flow as the flow travels toward the first row of turbine blades, and it requires substantial cooling. Energy is lost as the flow transitions from one component to the next, and cold air can leak into the hot gas path. Cold air leakage into the hot gas path through seals increases as seals wear due to vibration and ablation. Energy is also lost when the flow is redirected by the vanes.
The cooled components are expensive and complicated to manufacture due to the cooling structures, exacting tolerance requirements, and unusual shapes. Layers of thermal insulation for such cooled components may wear and can be damaged. Vane surfaces and thermal insulation layers thereon are prone to damage due to their oblique orientation relative to the flow. Such damage may necessitate component repair or replacement, which creates costs in terms of materials, labor, and downtime. Thermal stresses also reduce the service life of the underlying materials. Further, the vanes and seals require a flow of cooling fluid. This takes energy and creates more opportunities for heat-related component damage and associated costs.
Turbine vanes are produced in segments and then assembled together to form a ring. This requires additional seals between the vane components, through which there may be more cold air leakage into the hot gas path. Further, these configurations usually require assembly of the components directly onto the engine in confined areas of the engine, which is time consuming and difficult.